Steel has been widely used in forming a vehicular body. However, in addition to steel, light metal such as aluminum alloy has been recently used in order to reduce the weight of the vehicular body. Further, vehicular body members (e.g., an aluminum alloy roof panel, etc.) made from aluminum alloy, etc. can be applied to the vehicular body.
When a combination of dissimilar metals is used in the bonding portion of a body member, the dissimilar metals contact each other and permit conduction of electricity. This can accelerate corrosion.
The corrosion due to the contact of the dissimilar metals occurs because there is a voltage difference between these metals, which is caused by a difference in the ionization tendencies of the respective materials. Thus, corrosive currents flow between the dissimilar metals. In order to prevent such corrosion due to the contact of the dissimilar metals, several approaches have been suggested.
Japanese Laid-Open Patent Publication No. 2000-272541 discloses a bonding structure for a vehicular body member in which a first member made from steel and a second member made from aluminum or aluminum alloy are bonded by a bonding means such as a rivet or a reinforcing member, while interposing a seal material between the members.
Further, Japanese Laid-Open Patent Publication No. 2005-154844 discloses a method comprising the steps of immersing a bonding member of a iron-based material and an aluminum or aluminum alloy material into a solution containing a fluoro-complex ion and a zinc ion; and educing a metallic zinc around a bonding portion, wherein the metallic zinc has high density, rigidity and adhesiveness in addition to an ionization tendency ranging between those of aluminum and iron to provide an improved protection against corrosion due to the contact of the dissimilar metals at the bonding portion.